Who's the Sibling a sibling of?

[+ShardlessVessel]

I don't want authoritative answers, I want wild mass guessing. Who are the other siblings? Stormfather? Nightwatcher? Ba-Ado-Mishram? All of the above? None of the above? Just happens to be their name? One of the Heralds?

[MasterGhandalf]

Stormfather and Nightwatcher, I would assume. Stormfather is Honor's Cognitive Shadow/successor, Nightwatcher is described as Cutlivation's daughter and per WOB is to Cultivation as the Stormfather is to Honor, and the Sibling is depicted as a blending of Honor's and Cultivation's power. They're also all "siblings" in a more poetic sense, as the three Bondsmith spren. 

[Frustration]

It's the Stormfather and Nightwatcher.